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独占一行，不和其他元素待在同一行
能设置宽高
如果没有设置宽度, 那么默认和父元素一样宽如果设置了宽高, 那么就按照设置的来显示
常见的块级标签：div,p,h1-h6,ul,li,dl,dt,dd行级标签
能和其他元素待在同一行
不能设置宽高
如果没有设置宽度, 那么默认和内容一样宽行内元素是不可以设置宽度和高度的
常见的行级标签：a，span,strong,u,em行内块级标签
能和其他元素待在一行
能设置宽高
常见的行内块标签：img,input,textarea

文本标签学习
标题标签:
h1到h6:会将其中的数据加粗加黑显示.并且显示依次减弱.标题标签自带换行功能.(块级标签)
属性: align: center left right


水平线标签:
hr:会在页面中显示一条水平线,默认居中显示
属性:
width=”宽度” 设置水平线的宽度
size=”高度”  设置水平线的高度
color=”颜色” 设置水平线的颜色




换行符:  
br:告诉浏览器需要在此位置换行


空格符:
&amp;nbsp:告诉浏览器在此位置增加空格


权重标签:
b:会将 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/43808.html" title="HTML学习-1">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/wallhaven-j5jyjp.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="HTML学习-1"></a></div><div class="recent-post-info"><a class="article-title" href="/43808.html" title="HTML学习-1">HTML学习-1</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-10-03T02:27:25.000Z" title="发表于 2019-10-03 10:27:25">2019-10-03</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/43808.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/43808.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">
互联网的三大基石
URL:统一资源定位符.(唯一的定位一个网络资源)
HTTP:超文本传输协议.(规范浏览器和服务器之间数据交 互的格式)
HTML:超文本标记语言(有效的组织数据在浏览器端的显示)    
HTML的概念
概念:HTML是一种超文本标记语言
作用：需要将java在后台根据用户请求处理的请求结果在 浏览器中显示给户. 在浏览器中数据需要使用友好的格式展现给用户,HTML是告诉浏览器接收到的数据使用什么样的数据 组织形式进行显示.

HTML的文档声明
文件名.html 或者 文件名.htm
HTML的标准文档结构: 1234567&lt;html&gt;    &lt;head&gt;    &lt;/head&gt;    &lt;body&gt;    this is my first html.    &lt;/body&gt;&lt;/html&gt;
注意:HTML是由浏览器进行解析执行的

head标签
head标签中主要配置浏览器的配置信息
注意：防止markdown转义，标签前面加了”-“.实际不需要
title标签
告诉浏览器使用什么标题显示网页 
 ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/58900.html" title="LOG4J基础使用">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/wallhaven-1j66e3.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="LOG4J基础使用"></a></div><div class="recent-post-info"><a class="article-title" href="/58900.html" title="LOG4J基础使用">LOG4J基础使用</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-29T05:26:44.000Z" title="发表于 2019-09-29 13:26:44">2019-09-29</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/58900.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/58900.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">
LOG4J是什么？Log4j是Apache的一个开源项目，通过使用Log4j，我们可以控制日志信息输送的目的地是控制台、文件、GUI组件，甚至是套接口服务器、NT的事件记录器、UNIX Syslog守护进程等；我们也可以控制每一条日志的输出格式；通过定义每一条日志信息的级别，我们能够更加细致地控制日志的生成过程。最令人感兴趣的就是，这些可以通过一个配置文件来灵活地进行配置，而不需要修改应用的代码。

Log4j的作用
什么是日志：
日志是系统运行过程中后台输出信息，方便程序员进行系统运行的管控以及Bug的查找


什么是log4i
log4i是一个日志输出的插件，专门用来进行日志的管理的


传统方式获取日志
使用System.out.println()语句镜像后台打印
问题：
1.日志信息无法保存
2.无法显示完整日志信息
3.日志的显示没有级别所有的日志混在在一起显示（无法进行日志信息筛选）
4.日志显示格式不友好


解决：使用Log4j


使用log4j进行日志管理
特点：
1.日志可以单独保存在文件中
2.可以获取完整的日志信息
3.可以进行日志显示的筛选
4.格式友好
 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/8601.html" title="Java反射学习-1">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/img/20200418114719.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java反射学习-1"></a></div><div class="recent-post-info"><a class="article-title" href="/8601.html" title="Java反射学习-1">Java反射学习-1</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T13:13:54.000Z" title="发表于 2019-09-28 21:13:54">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/8601.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/8601.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">反射的概念和作用:
JAVA反射机制是在运行状态中，对于任意一个实体类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意方法和属性；这种动态获取信息以及动态调用对象方法的功能称为java语言的反射机制。
反射的概念：万事万物皆对象,类也是对象.
引用:通过反射创建类对象和使用类对象.
问题:
传统方式创建对象:new 类名();,前提是必须预先知道要使用的类.但是,如果无法确定要执行的对象怎么办?
如果要修改使用的类,必须修改源码.


解决:使用反射.

反射获取类对象
Class.forName();———根据全限定路径获取(必须会)
Class cla01 = Class.forName(“Bean.Person”);


对象名.getClass();——-根据对象获取
Class cla02 = Person.class;


类名.class—————根据类名获取
Class cla03 = new Person().getClass();


获取类对象的相关方法函数
获取类对象的包名：cla01.getPackage()
获取类对象的修饰符：cla ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/60981.html" title="JDBC操作学习-5">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/wallhaven-nm97v9.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="JDBC操作学习-5"></a></div><div class="recent-post-info"><a class="article-title" href="/60981.html" title="JDBC操作学习-5">JDBC操作学习-5</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T06:49:14.000Z" title="发表于 2019-09-28 14:49:14">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox"></i><a class="article-meta__categories" href="/categories/Java/">Java</a><i class="fas fa-angle-right"></i><a class="article-meta__categories" href="/categories/Java/JDBC/">JDBC</a></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/60981.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/60981.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">JDBC的封装
问题:在数据库操作方法中关于驱动加载和数据库连接对象的代码是重复的.会造成修改数据源特别麻烦.

解决1:将jdbc参数在功能类中提取为全局变量


问题2:如果使用解决方式1解决后,修改了数据源则必须重启程序.而开发过程中尽量要求,在不重启程序的情况下完成对代码的参数的修改.

解决2:将jdbc参数存储到properties属性配置文件中,封装工具类进行获取.


知识点:

properties文件是专门用来存储属性配置的文件,格式要求必须是键值对,以=号隔开.一行一组键值对,并且不能使用分号结尾.可以使用Properties对象来进行读取该文件的内容.    


使用:

创建java工具类（Util-JdbcUtil）
创建jdbc参数静态变量
创建静态代码块
创建properties对象（db.properties）
获取properties文件流对象
加载属性配置文件
获取jdbc参数并赋值给静态变量
加载驱动
创建获取Connection对象的静态方法
创建获取PreparedStatement对象的静态方法
创建获取Statement对象的静态方法
 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/12020.html" title="JDBC操作学习-4">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/博客封面9.png" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="JDBC操作学习-4"></a></div><div class="recent-post-info"><a class="article-title" href="/12020.html" title="JDBC操作学习-4">JDBC操作学习-4</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T06:29:44.000Z" title="发表于 2019-09-28 14:29:44">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox"></i><a class="article-meta__categories" href="/categories/Java/">Java</a><i class="fas fa-angle-right"></i><a class="article-meta__categories" href="/categories/Java/JDBC/">JDBC</a></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/12020.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/12020.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">使用PreparedStatement对象完成数据库的增删改查
特点:
防止sql注入
提升sql语句的执行效率(当批量执行同一类型的sql语句时)


使用:
创建集合或者实体类对象(可选-查询)    
加载驱动
获取连接对象
设置手动数据提交(可选–增删改)
创建sql命令
获取sql命令对象
给占位符赋值
执行sql语句
遍历执行结果(可选–查询)
提交数据(可选–增删改)
回滚数据(可选-增删改)
关闭资源
返回结果(封装成方法)



123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100public class UserDaoImpl &#123;		//查询用户信息	public User getUserInfo(String uname,Str ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/60597.html" title="JDBC操作学习-3">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/博客封面9.png" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="JDBC操作学习-3"></a></div><div class="recent-post-info"><a class="article-title" href="/60597.html" title="JDBC操作学习-3">JDBC操作学习-3</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T04:51:42.000Z" title="发表于 2019-09-28 12:51:42">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox"></i><a class="article-meta__categories" href="/categories/Java/">Java</a><i class="fas fa-angle-right"></i><a class="article-meta__categories" href="/categories/Java/JDBC/">JDBC</a></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/60597.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/60597.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">JDBC事务管理事务:一个事件的完成需要几个子操作的联合完成,只要有一个子操作执行失败,则数据回滚到原始状态,都成功则提交数据.


转账业务

张三给李四转账1000元.

注意:JDBC中的事务是自动提交的.

问题:如果在业务的处理过程中,某条Sql语句执行失败,但是数据已经被更改了.

解决:设置JDBC的事务为手动提交.sql语句都执行成功后再统一提交,只要有失败的就回滚.

使用:conn.setAutoCommit(false)//设置为手动提交

使用try catch进行SQL命令执行的异常处理

try中是使用conn.commit() 提交数据
catch中使用conn.rollback()回滚数据





123456789101112131415161718192021222324252627public class TestTran &#123;	public static void main(String[] args) throws ClassNotFoundException, SQLException &#123;		//加载驱动			Class. ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/11380.html" title="JDBC操作学习-2">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/博客封面15.png" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="JDBC操作学习-2"></a></div><div class="recent-post-info"><a class="article-title" href="/11380.html" title="JDBC操作学习-2">JDBC操作学习-2</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T02:54:59.000Z" title="发表于 2019-09-28 10:54:59">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox"></i><a class="article-meta__categories" href="/categories/Java/">Java</a><i class="fas fa-angle-right"></i><a class="article-meta__categories" href="/categories/Java/JDBC/">JDBC</a></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/11380.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/11380.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">JDBC的基本使用流程:
1 导入jar包:
oracle安装路径\app\oracle\product\11.2.0\server\jdbc\lib
导入ojdbc6.jar,在项目上右键 builder path–&gt;add to builder path.


2 加载驱动 
Class.forName(“oracle.jdbc.driver.OracleDriver”);
作用:初始化加载jdbc类到java虚拟机.
注意:ojdbc6.jar使用此包该句可以省略不写.        


3 获取数据库连接对象
Connection conn =DriverMananger.getConnection(“url”,”username”,”password”);
参数含义:
url:表示要连接的数据地址
username:数据库的用户名
password:数据库的密码


作用:
连接到指定的数据库并返回连接对象.




4 创建sql命令对象
Statement stmt=conn.createStatement();
作用:
编译,发送SQL命令




5 创建sq ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/11572.html" title="JDBC操作学习-1">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/github/img/img/荒鲸.png" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="JDBC操作学习-1"></a></div><div class="recent-post-info"><a class="article-title" href="/11572.html" title="JDBC操作学习-1">JDBC操作学习-1</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T02:28:07.000Z" title="发表于 2019-09-28 10:28:07">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox"></i><a class="article-meta__categories" href="/categories/Java/">Java</a><i class="fas fa-angle-right"></i><a class="article-meta__categories" href="/categories/Java/JDBC/">JDBC</a></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/11572.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/11572.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">JAVA的数据获取方式:
直接声明变量并赋值.
Scanner类控制台输入
IO流(将硬盘存储中的数据读取到java中)
scoket+io
从数据库中获取
JDBC的概念:
问题:
java和数据库之间的沟通不一致    


解决:
数据库厂商对外提供java支持的接口


使用:
创建类实现接口(操作数据库)
数据库厂商对外提供了数据库操作的驱动包.(翻译官)


结论:
JDBC其实就是数据厂商对外提供的能够对自己的数据进行操作的驱动包也就是jar文件.


JDBC的使用:
jdbc完成新增
jdbc完成修改
jdbc完成删除
jdbc的事务
jdbc完成查询
jdbc的MVC思想



</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/35176.html" title="MySQL数据库-2">     <img class="post_bg" data-lazy-src="https://qiniu.codekylin.cn/img/20200708172722.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="MySQL数据库-2"></a></div><div class="recent-post-info"><a class="article-title" href="/35176.html" title="MySQL数据库-2">MySQL数据库-2</a><div class="article-meta-wrap"><span class="post-meta-date"><i class="far fa-calendar-alt"></i><span class="article-meta-label">发表于</span><time datetime="2019-09-28T02:06:20.000Z" title="发表于 2019-09-28 10:06:20">2019-09-28</time></span><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-comments"></i><a href="/35176.html#post-comment" itemprop="discussionUrl"><span class="valine-comment-count" data-xid="/35176.html" itemprop="commentCount"></span></a><span class="article-meta-label"> 条评论</span></span></div><div class="content">数据类型
数值类型
整数类型
smallint, 2 字节
int, 4 字节
Integer, int 的同义词
bigint, 8 字节


浮点数
float, 4 字节
double, 8 字节




字符类型
char, 不可变长度
varchar, 可变长度
等同于oracle中的char与varchar2区别
char的存储效率高于varchar(varchar2)
char是开辟指定大小的内存空间，varchar(varchar2)是根据数据大小来开辟空间的大小


日期时间类型
date, yyyy-mm-dd（同oracle书写格式不一样）
datetime, yyyy-mm-dd hh:mi:ss
time, hh:mi:ss
timestamp, 更精确的时间
year, yyyy


其他类型
blob, 存放二进制文件
text, 存放大量文本信息



SQL语句上的区别
关于delete
Oracle 中的语法是 delete [from], from 可以省略, 但是MySQL 中, 不能省略 from


关于外连接
MySQL 中不能使用(+)符 ...</div></div></div><nav id="pagination"><div class="pagination"><a class="extend prev" rel="prev" href="/page/33/#content-inner"><i class="fas fa-chevron-left fa-fw"></i></a><a class="page-number" href="/">1</a><span class="space">&hellip;</span><a class="page-number" href="/page/33/#content-inner">33</a><span class="page-number current">34</span><a class="page-number" href="/page/35/#content-inner">35</a><span class="space">&hellip;</span><a class="page-number" href="/page/37/#content-inner">37</a><a class="extend next" rel="next" href="/page/35/#content-inner"><i class="fas fa-chevron-right fa-fw"></i></a></div></nav></div><div class="aside-content" id="aside-content"><div class="card-widget card-info"><div class="card-info-avatar is-center"><img class="avatar-img" data-lazy-src="https://qiniu.codekylin.cn/img/20200807181526.jpg" onerror="this.onerror=null;this.src='https://qiniu.codekylin.cn/github/img/friend_404.gif'" alt="avatar"/><div 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